Process for stabilizing jet fuels



July 5, 1960 C. E. THOMPSON PROCESS FOR STABILIZING JET FUELSHYDROTREATING EL. ZONE Filed March 15, 1957 PURGE GAS STRIPPERADSORPTlON ZONE- l4 PURGE GAS 1 Chorles'E. Thorhpsoh Inventor By a 1 aPatent Attorney United States. Patent PROCESS FOR STABILIZING FUELSCharles E. Thompson, Fanwood, N.J., assignor to Esso Research andEngineering Company, a corporation of Delaware Filed Mar. 15, 1957, Ser.No. 646,288

8 Claims. (Cl. 208-212) The present invention relates to the preparationof fuels adapted to be used in internal combustion and jet engines. Moreparticularly, the present invention relates to an improved process forthe preparation of jet fuels that are thermally stable and less subjectto deteriorative changes and deposit formation than are presentlyavailable by conventional preparations.

In the operation of both internal combustion and jet engines, a seriousproblem existing at the present time is the formation of enginedeposits, in which fuels play an important role. Furthermore,particularly in jet engines, a further problem arises in the plugging offuel filters at low temperatures. Carbonaceous deposits in thecombustors of a jet engine are very undesirable in that they disrupt thedesired fuel spray patterns in the combustors, cause warping of theliners and thus reduce the amount of power that can be generated.Furthermore, jet fuels must be thermally stable as they are circulatedthrough a heat exchanger with the oil from the engine; if unstableconstituents are present, the heat exchangers, screens and nozzles inthe fuel system become clogged with the polymeric material formed, thuscausing malfunctioning of the engine.

The military services have set up a number of jet fuel specifications inwhich an effort has been made to define fuels that minimize depositformation and other difiiculties that have been encountered in theoperation of jet aircraft. Specification of three such fuel types aregiven in Table I.

Jet fuels for use in commercial aircraft are normally obtained bysegregating selected refinery streams boiling in the naphtha andkerosene range, preferably having substantial paraflinic content. Thesefuels are not stable enough for use in supersonic aircraft because ofthe extremely high heat stability required. Treating methods employedfor stabilizing hydrocarbons for normal service have not been foundsatisfactory for stabilizing jet fuels. thermally stable jet fuel. Suchprocesses are not only expensive, but entail substantial product lossesand are not suited for large scale plant production.

It has now been found that highly satisfactory thermally stable jetfuels may be prepared by treating selected hydrocarbon distillatesboiling in the range of 200 to 600 F. with hydrogen in the presence of acatalyst such as cobalt molybdate, molybdenum disulfide or molybdenasupported on alumina where the proportion of CoMoO M05 or M varies from5 to 25% and the alumina or alumina-silica base varies from 95 to 75%.In this step the temperature is in'the range of 300-750 F., the pressuremay be in the range of 50-1000 p.s.i.g., the feed rate may be variedfrom 0.5 to v./hr./v. and the amount of hydrogen may vary from 50-6000s.c.f./b. The product flom this treatment is then either stripped withnitrogen or other inert gas, or caustic washed to remove hydrogensulfide, or both, and treated with an adsorbent material such asactivated diatomaceous earth or other Only servere acid treating hasproduced a adsorbent material such as activated carbon or alumina.

2,944,032 Patented July 5, 1960 TABLE 1 MIL-F-5624O SIP-4 .TP-5

Gravity, API Freezing Point, F "max" Aromatics, Vol. Percent Oleflns,Vol. Percent..- Smoke Vol. Index Smoke Point, mm Existant Gum, mg./1111.. Potential Gum, mg./100 ml. Sulfur, Total Wt. Peroent- MercaptanSulfur, Wt. Percen Flash Point, F Heating Value, Net B.t.u./lb

r Aniline-Gravity Product m1n.- Reid Vapor Pressure, p at WaterTolerance, ml Corrosion, Copper Strip 20 max 7 7 6 max- 10 Lt. Tan

1 0r pass doctor test.

Mar. pressure drop in CFR fuel eoker after 5 hours at. 6#/hr. fullflow-rate, 400,F. fuel temperature, 500 F. filter temperature.Equivalent to a merit rating of 510.

The oil is treated with 1.0 to 10% by weight of the adsorbent material.The jet fuel is then separated from the adsorbent material by decanting,filtering or centrifuging. The resulting jet fuel is exceptionallythermally stable.

In accordance with the flow sheet of the present invention, -a selectedpetroleum feedstock containing hydrocarbons which boil in the heavynaphtha and kerosene range is passed via line 2 to a conventionalhydrotreating unit 4, and is there treated with hydrogen under theconditions enumerated heretofore.

The hydrotreating catalysts that-can be employed in the hydrofininginclude 5-15% molybdena oxide on activated alumina, mixtures of cobaltoxides (2-6 Wt. percent) and molybdenum oxides (6-15 wt. percent), anequivalent amount of cobalt molybdate on activated alumina, and othersulfur resistant hydrogenation catalysts such as those of the nickeltungsten sulfide type and unsupported molybdenum disulfide.

Regeneration of the fixed bed catalyst may be required periodically,depending largely upon the nature of the feed stock. This regenerationis conveniently carried out at a temperature of about 750-1000 F., withan oxygencontaining gas.

In the hydrotreating operation, the oil and hydrogen are contacted withcatalyst by continuous flow through vessel 4 packed with catalyst. Theoil feed to the reactor is preheated to the required temperature bymeans of a furnace or similar means. Hydrogen may or may not be heatedprior to feeding to the reactor depending on the quantity used. Thedegree of' contact of oil saturated with hydrogen with the catalyst isdetermined by the ratio of the oil flow rate to the catalyst volume.

From hydrotreating zone 4 the liquid is passed via line 6 to stripper 8to remove residual H 8, which is an undesirable constituent in jetfuels. Alternatively or in addition, the hydrotreated product may becaustic washed to remove acidic sulfur. The sulfur-free hydrocarbonproduct, cooled to a temperature belowabout 100 F. in cooler 12 ispassed via line 10 to an adsorption zone 14.

. It isimportant that adsorption be carried out in the liquid phase.Vapor phase adsorption will not provide the thermally stable jet fuel.In zone 14 the liquid is contacted in a slurry with 1 to' of anadsorbent. The temperature in zone 14 is in therange of 60 to 100 'F.,and

' substantially any high surface area adsorbenusuchas activateddiatomaceous earth, other siliceous material, char, alumina, zeolitesand the like, may be employed. The oil may be treated with 1.0 to 10% byweight of the adsorbent. a

The jet fuel is then separated from the adsorbent material bydecantation, filtration or centrifuging and is withdrawn through line16. 'Theresulting fuel is thermally stable." 7 a a 7 a a The advantagesof the present invention will be better understood by reference to thefollowing examples:

Exa mp le Specifications defining'the'necessary levels of thermalstability of jet fuel which Lcanibe determined on a labora-. tory scaleare based on the CFR fuel coker rig, a device for measuring fuel thermalstability. High stability jet fuelsfo'f the JP-j-Sj aind JP-6' typqhavea specification of a CFR fuel coker merit ratingof500. The CFR fuelcoker is essentially a scaled down version of a full scale turbo enginefuel system which simulates the fuel/oil heat exchanger and combustornozzle of a jet engine. Fuel is pumped at predetermined rates through ahot heat- The substantially improved-product employing thecombinationsteps is immediately apparent; Thus it can be seen from theabove table that the individual treating steps described have not beeneffective in producing a thermally stable jet fuel. Evenon the kerosenewhich had a 230 merit rating untreated it was necessary to use an oleumtreat of 59 lb./bbl. to obtain a stable fuel.

Even higher acid treating'would be necessary to stabilize the othersample of kerosene. These high acid treats are expensive and not suitedto large scale plant production! 0 Example 2 v To demonstratethe-importance of liquid phase adsorption, further experimental work wascarried out "'1 rating of this fuel was only 405, a value lowerthan'spe'ciexchanger tube which simulates the hot fuel line sections ofthe engine. The fuel then passes through a heated 20 micron metal filtersection wlgrich represents the nozzle area orsmall fuel passages in thehot section of the engine where fuel degradation products may becometrapped. Thefilter traps. fuel degradation products formed during thetest. Fuel degradation is measured by the increased pressure drop acrossthe metal filter and by a'visualrat- .ing of the varnish-likedepositslaid down on the hot heat exchanger .tube.- Typical pressure drop dataare translated into an arbitrary merit rating.

A- series of tests were carried out whereinKa) a distillate fuel boilingin the range of 345 to 512. F., having an API gravity of 42.4 at 60 F.and a freezing point of 48 a F., was hydrotreated in the presence of acobalt molybobtained:

EXPERIMENTAL PROCESS TO IMPROVE THERMAL STABILITY OFR Fuel Coker 1Process Merit Tube Rating Deposits Targ 500 Clean to Lt.

Tan.

Untreated ZIP-5 Stock 10 Fail.

Hydrotreated 235-535 Variable.

3 Wt. Percent Clay Contact 300 Fail.

Oxidized (Air at 170 F.). 160 Fall.

Sodium Treating 415 Pass.

SO; Extracted 300 Fall.

Hydrotreated+3 Wt. Percent Clay 850 Pass.

Contact. 7

Untreated JP-5v Stock 230 Fall;

Hydrotr eating V 405 3% Oleum (19. .lbbl 355 9% Oleum (591b./bbl.)-.-550 Hydrotreating+3 Wt. Percent Cla 700 Pass.

Contact. V

' 1 High temperature test condition's:;400 F. fuel temperature; 500 F.

filter temperature; 6'1b./hr..fue1 now.

R 1 hr. of stirring with Super Filtrol at 74 11. V7

wherein the same 'feed'was hydrotreated in the presence of acobalt-molybdate on alumina catalyst at 565 3.7 v./hr./v., 3500 -s.c.f.of l-l /barrehat .750 psig The total product from the hydrotreating stepwas passed directly to the adsorption 'stagewhere the conditions were480 F., a feed rate of 5.5 v./ hr./v.,'and a pressure of 0.-;p.s.i.g.

Theproduct from" this experimentwas evalnatedlby the CFR fuel coker rigtest for thermal stability. The

fication forjet fuel and considerably lower than the850 rating obtainedby-the process of the present invention.

I d-another modification of the present invention, the hydrotreatingstep is carried out with a low surface area catalyst having goodhydrogenation activity. Normal treating catalyst may contain from .75 toalumina or silica alumina base.

This material is active as an isomerizing agent for 7 hydrocarbonmaterials and capable at the temperatures employed of forminghydrocarbon products which. will 7 polymerize and, therefore, be lessthermally stable than before treating as for example, the isomerizationand dehydrogenation of tetralin to methyl-indene. Use of a catalysthaving a very low surface area'and not contain: ing alumina or silicaavoids thisreaction. Such catalysts as unsupported molybdenum disulfideor nickel tungsten' sulfide are superior for hydrotreating a jet fuelfor thermal stability for two reasons. They do not have theisomerization activity of alumina supported catalysts and they havegreater hydrogenation activity. The greater hydrogenation activity isbeneficial in that the hydrogenated products-have a lowered smokingtendency' This is a characteristic that is to be desired in jet fuels.What'is claimed is: 1. An improved process for refining a hydrocarbonfuel to produce a highly thermally stable product which comprisessegregating a refining stream boiling in the range of about 200-600" F.and containing sulfur, catalytically hydrotreating said stream in thepresence. ofa

hydrotreating catalyst at a temperature of from about- 300750 F., andpressure of 50-1000 p.s.i.g., removing 7 sulfur-containing products fromsaid hydrotreating material, condensing said hydro treated product,treating said liquefied product with an adsorbent having a high surfacearea, and recovering a thermally stable fuel.

2. The process of claim 1 wherein said catalyst is a molybdenumcompound.

3. The process of claim 1, wherein said hydrotreated product is cooledto at least v F. prior to treatment withrsaid adsorbent. v

'4. The process of claim 3 wherein said adsorbent is a diatomaceousearth.

5. The process of claim 3. wherein said adsorbent is a clay.

6. An] improved process for preparing a thermally stable jet fuel whichcomprises hydrot reating a predominantly paraflinic hydrocarbon fractioncontaining sulfur and boiling in the heavy naphtha and kerosene range inthe presence of an unsupported hydrotreating catalyst at hydrotreatingconditions of temperature and pressure,

cooling said hydrotreated product to at least 100 F., and treating saidproduct at a temperature of about 60100 F., in the liquid phase with 1to 10% by weight of an adsorbent having a high surface area.

7. The process of claim 6 wherein said scrubbing is by an inert gas.

8. The process of claim 6 wherein hydrotreated prod- Y 110: is causticscrubbed.

UNITED STATES PATENTS Murray et a1. Sept. 6, 1955 Fenske et a1. Oct. 9,1956 Annable et a1. Nov. 6, 1956 Scovill et al. July 16, 1957

1. AN IMPROVED PROCESS FOR REFINING A HYDROCARBON FUEL TO PRODUCE AHIGHLY THERMALLY STABLE PRODUCT WHICH COMPRISES SEGREGATING A REFININGSTREAM BOILING IN THE RANGE OF ABOUT 200-300*F. AND CONTAINING SULFUR,CATALYTICALLY HYDROTREATING SAID STREAM IN THE PRESENCE OF AHYDROTREATING CATALYST AT A TEMPERATURE OF FROM ABOUT 300-750* F., ANDPRESSURE OF 50-1000 P.S.I.G., REMOVING SULFUR-CONTAINING PRODUCTS FROMSAID HYDROTREATING MATERAIL, CONDENSING SAID HYDROTREATED PRODUCT,TREATING SAID LIQUENFIED PRODUCT WITH AN ADSORBENT HAVING A HIGH SURFACEAREA, AND RECOVERING A THERMALLY STABLE FUEL.